docs/manual/pkg-cmake.txt: fix _INSTALL_STAGING_OPTS/_INSTALL_TARGET_OPTS description

Since commit dfcc18f84b0d90b0ed5937bac3c4b12aba086cd5 cmake-package
_INSTALL_STAGING_OPTS/_INSTALL_TARGET_OPTS use 'install/fast'
instead of 'install', adjust documentation accordingly.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 0c80a0da9aaf1e051ceb1a319ebef7a933674ca9)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/adding-packages-cmake.txt

@@ -128,12 +128,12 @@ typical packages will therefore only use a few of them.
 
 * +LIBFOO_INSTALL_STAGING_OPTS+ contains the make options used to
   install the package to the staging directory. By default, the value
-  is +DESTDIR=$(STAGING_DIR) install+, which is correct for most
+  is +DESTDIR=$(STAGING_DIR) install/fast+, which is correct for most
   CMake packages. It is still possible to override it.
 
 * +LIBFOO_INSTALL_TARGET_OPTS+ contains the make options used to
   install the package to the target directory. By default, the value
-  is +DESTDIR=$(TARGET_DIR) install+. The default value is correct
+  is +DESTDIR=$(TARGET_DIR) install/fast+. The default value is correct
   for most CMake packages, but it is still possible to override it if
   needed.